Ventilation, i.e., the removal of excess heat and moisture from within the footwear, is one of the few areas where performance of modern footwear that remains unsatisfactory. Although there is an extensive prior art concerning the forced air ventilation of footwear, typical forced air ventilation systems are costly and difficult to manufacture, have poor durability, or are otherwise incapable of circulating a sufficient amount of air to cool the wearer's foot effectively.
To reduce the cost and difficulty in footwear having a forced air ventilation system, ventilated footwear been proposed in which the entire ventilation system is incorporated in a removable insole. Such ventilating insoles are disclosed in U.S. Pat. No. 3,331,146 (disclosing a chamber in the heel of an insole with duct leading into the front of foot and a second duct rising above the foot-enclosing upper); U.S. Pat. No. 4,776,110 (disclosing an insole with a chamber in the heel, multiple distribution channels and an air guide for exchanging air through the side of the foot-enclosing upper); U.S. Pat. No. 5,068,981 (disclosing a heel chamber incorporating a mechanical spring and ducts configured to vent through the side walls of the foot-enclosing upper); U.S. Pat. No. 5,195,254 (disclosing a molded insole and an assisting "blast device"); and U.S. Pat. No. 5,333,397 (disclosing a kidney-shaped air clamber position at the rear and inner periphery of the insole). Such insoles with ventilation system, however, have several intrinsic disadvantages such as:
(1) the volume of air that can be circulated by an insole device is severely limited by the thickness of the insole; PA1 (2) the periodic compression of the insole pump requires the wearer's foot to move vertically relative to the interior sides of the footwear, resulting in friction, irritation, and possible blisters; PA1 (3) the re-circulation of the air contained within the footwear provides little long-term benefit, and the process itself may even cause the interior temperature to rise; PA1 (4) insoles adapted to exchange air with the external environment are complex and often affect the design, manufacture, and aesthetic aspects of the footwear; and PA1 (5) the space and material limitations of the insole design result in a rapid degradation of their cushioning and air-pumping capabilities.
Another footwear ventilation system embeds the ventilation system in the sole structure of footwear with relatively thick, resilient midsole components. U.S. Pat. No. 5,515,622 discloses a ventilation system comprised of numerous separate components in the midsole of an athletic footwear. Although this approach allows for larger pumped air volumes and eliminates some friction, this approach also complicates the manufacturing of the footwear. Furthermore, for practical reasons the pumped air volume is significantly limited to about 20 cubic-centimeters (cc) that is insufficient to cool the wearer's foot effectively. U.S. Pat. No. 5,010,661 also disloses a ventilation system in the sole of a shoe, in this case a unidirectional ventilation sytem in which air is pumped into a cavity in the heel of the shoe, and then pumped out through outlets in the front part of the shoe.
A third improvement to footwear ventilation system is a hybrid of the two approaches described above. For example, U.S. Pat. No. 5,408,760 discloses a removable molded device comprising a small compressible air chamber and two non-return valves fitted into a cavity in the sole under the wearer's forefoot. Pumped air volume in this configuration, however, remains quite small and thus incapable of cooling the wearer's foot effectively.
As described above, there is still an unsatisfied need for a simple forced air ventilation system that is inexpensive and easy to manufacture, durable, and capable of pumping sufficient air to effectively cool a person's feet.